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Revision 1.6 by root, Thu Mar 22 23:24:18 2007 UTC vs.
Revision 1.109 by root, Sat Jul 19 04:21:32 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
12	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
13	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
14		47
15	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
16	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
17	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See COMPARISON, below, for a comparison to some other JSON modules.
22		55
		56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		57	vice versa.
		58
23	=head2 FEATURES	59	=head2 FEATURES
24		60
25	=over 4	61	=over 4
26		62
27	=item * correct handling of unicode issues	63	=item * correct Unicode handling
28		64
29	This module knows how to handle Unicode, and even documents how it does so.	65	This module knows how to handle Unicode, documents how and when it does
		66	so, and even documents what "correct" means.
30		67
31	=item * round-trip integrity	68	=item * round-trip integrity
32		69
33	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only data types supported
34	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
35	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
36		75
37	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
38		77
39	There is no guessing, no generating of illegal JSON strings by default,	78	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	79	and only JSON is accepted as input by default (the latter is a security
		80	feature).
41		81
42	=item * fast	82	=item * fast
43		83
44	compared to other JSON modules, this module compares favourably.	84	Compared to other JSON modules and other serialisers such as Storable,
		85	this module usually compares favourably in terms of speed, too.
45		86
46	=item * simple to use	87	=item * simple to use
47		88
48	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an object
49	interface.	90	oriented interface interface.
50		91
51	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
52		93
53	You can choose between the most compact format possible, a pure-ascii	94	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	95	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	96	(for when your transport is not 8-bit clean, still supports the whole
		97	Unicode range), or a pretty-printed format (for when you want to read that
		98	stuff). Or you can combine those features in whatever way you like.
56		99
57	=back	100	=back
58		101
59	=cut	102	=cut
60		103
61	package JSON::XS;	104	package JSON::XS;
62		105
63	BEGIN {	106	use strict;
		107
64	$VERSION = '0.2';	108	our $VERSION = '2.222';
65	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
66		110
67	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		112
		113	sub to_json($) {
70	require XSLoader;	114	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	116	}
73		117
		118	sub from_json($) {
		119	require Carp;
		120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
74	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
75		127
76	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
77	exported by default:	129	exported by default:
78		130
79	=over 4	131	=over 4
80		132
81	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
82		134
83	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		137
87	This function call is functionally identical to C<< JSON::XS->new->utf8	138	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	Except being faster.
		143
90	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
91		145
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	148	reference. Croaks on error.
95		149
96	This function call is functionally identical to C<< JSON::XS->new->utf8	150	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	Except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
98		164
99	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode code point.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
100		215
101	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
102		217
103	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
112		227
113	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	229	be chained:
115		230
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
118		233
119	=item $json = $json->ascii ($enable)	234	=item $json = $json->ascii ([$enable])
120		235
		236	=item $enabled = $json->get_ascii
		237
121	If C<$enable> is true, then the C<encode> method will not generate	238	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	239	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	240	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
125		245
126	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
127	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
128		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	258	=> ["\ud801\udc01"]
131		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		287
132	=item $json = $json->utf8 ($enable)	288	=item $json = $json->utf8 ([$enable])
133		289
		290	=item $enabled = $json->get_utf8
		291
134	If C<$enable> is true, then the C<encode> method will encode the JSON	292	If C<$enable> is true (or missing), then the C<encode> method will encode
135	string into UTF-8, as required by many protocols, while the C<decode>	293	the JSON result into UTF-8, as required by many protocols, while the
136	method expects to be handled an UTF-8-encoded string. Please note that	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
137	UTF-8-encoded strings do not contain any characters outside the range	295	note that UTF-8-encoded strings do not contain any characters outside the
138	C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
139		299
140	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
141	string as a (non-encoded) unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
142	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
143	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
144		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
		308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		317
145	=item $json = $json->pretty ($enable)	318	=item $json = $json->pretty ([$enable])
146		319
147	This enables (or disables) all of the C<indent>, C<space_before> and	320	This enables (or disables) all of the C<indent>, C<space_before> and
148	C<space_after> (and in the future possibly more) flags in one call to	321	C<space_after> (and in the future possibly more) flags in one call to
149	generate the most readable (or most compact) form possible.	322	generate the most readable (or most compact) form possible.
		323
		324	Example, pretty-print some simple structure:
150		325
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	326	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	327	=>
153	{	328	{
154	"a" : [	329	"a" : [
155	1,	330	1,
156	2	331	2
157	]	332	]
158	}	333	}
159		334
160	=item $json = $json->indent ($enable)	335	=item $json = $json->indent ([$enable])
161		336
		337	=item $enabled = $json->get_indent
		338
162	If C<$enable> is true, then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
163	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	341	into its own line, indenting them properly.
165		342
166	If C<$enable> is false, no newlines or indenting will be produced, and the	343	If C<$enable> is false, no newlines or indenting will be produced, and the
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
168		345
169	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
170		347
171	=item $json = $json->space_before ($enable)	348	=item $json = $json->space_before ([$enable])
172		349
		350	=item $enabled = $json->get_space_before
		351
173	If C<$enable> is true, then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
174	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
175		354
176	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
177	space at those places.	356	space at those places.
178		357
179	This setting has no effect when decoding JSON strings. You will also most	358	This setting has no effect when decoding JSON texts. You will also
180	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
181		360
		361	Example, space_before enabled, space_after and indent disabled:
		362
		363	{"key" :"value"}
		364
182	=item $json = $json->space_after ($enable)	365	=item $json = $json->space_after ([$enable])
183		366
		367	=item $enabled = $json->get_space_after
		368
184	If C<$enable> is true, then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
185	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
186	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	372	members.
188		373
189	If C<$enable> is false, then the C<encode> method will not add any extra	374	If C<$enable> is false, then the C<encode> method will not add any extra
190	space at those places.	375	space at those places.
191		376
192	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
193		378
		379	Example, space_before and indent disabled, space_after enabled:
		380
		381	{"key": "value"}
		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
194	=item $json = $json->canonical ($enable)	430	=item $json = $json->canonical ([$enable])
195		431
		432	=item $enabled = $json->get_canonical
		433
196	If C<$enable> is true, then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
197	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
198		436
199	If C<$enable> is false, then the C<encode> method will output key-value	437	If C<$enable> is false, then the C<encode> method will output key-value
200	pairs in the order Perl stores them (which will likely change between runs	438	pairs in the order Perl stores them (which will likely change between runs
201	of the same script).	439	of the same script).
202		440
203	This option is useful if you want the same data structure to be encoded as	441	This option is useful if you want the same data structure to be encoded as
204	the same JSON string (given the same overall settings). If it is disabled,	442	the same JSON text (given the same overall settings). If it is disabled,
205	the same hash migh be encoded differently even if contains the same data,	443	the same hash might be encoded differently even if contains the same data,
206	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
207		445
208	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
209		447
210	=item $json = $json->allow_nonref ($enable)	448	=item $json = $json->allow_nonref ([$enable])
211		449
		450	=item $enabled = $json->get_allow_nonref
		451
212	If C<$enable> is true, then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
213	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
214	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	455	values instead of croaking.
216		456
217	If C<$enable> is false, then the C<encode> method will croak if it isn't	457	If C<$enable> is false, then the C<encode> method will croak if it isn't
218	passed an arrayref or hashref, as JSON strings must either be an object	458	passed an arrayref or hashref, as JSON texts must either be an object
219	or array. Likewise, C<decode> will croak if given something that is not a	459	or array. Likewise, C<decode> will croak if given something that is not a
220	JSON object or array.	460	JSON object or array.
221		461
		462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		463	resulting in an invalid JSON text:
		464
		465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		466	=> "Hello, World!"
		467
		468	=item $json = $json->allow_unknown ([$enable])
		469
		470	=item $enabled = $json->get_allow_unknown
		471
		472	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		473	exception when it encounters values it cannot represent in JSON (for
		474	example, filehandles) but instead will encode a JSON C<null> value. Note
		475	that blessed objects are not included here and are handled separately by
		476	c<allow_nonref>.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters anything it cannot encode as JSON.
		480
		481	This option does not affect C<decode> in any way, and it is recommended to
		482	leave it off unless you know your communications partner.
		483
		484	=item $json = $json->allow_blessed ([$enable])
		485
		486	=item $enabled = $json->get_allow_blessed
		487
		488	If C<$enable> is true (or missing), then the C<encode> method will not
		489	barf when it encounters a blessed reference. Instead, the value of the
		490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		491	disabled or no C<TO_JSON> method found) or a representation of the
		492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		493	encoded. Has no effect on C<decode>.
		494
		495	If C<$enable> is false (the default), then C<encode> will throw an
		496	exception when it encounters a blessed object.
		497
		498	=item $json = $json->convert_blessed ([$enable])
		499
		500	=item $enabled = $json->get_convert_blessed
		501
		502	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		503	blessed object, will check for the availability of the C<TO_JSON> method
		504	on the object's class. If found, it will be called in scalar context
		505	and the resulting scalar will be encoded instead of the object. If no
		506	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		507	to do.
		508
		509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		510	returns other blessed objects, those will be handled in the same
		511	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		512	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		513	methods called by the Perl core (== not by the user of the object) are
		514	usually in upper case letters and to avoid collisions with any C<to_json>
		515	function or method.
		516
		517	This setting does not yet influence C<decode> in any way, but in the
		518	future, global hooks might get installed that influence C<decode> and are
		519	enabled by this setting.
		520
		521	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		522	to do when a blessed object is found.
		523
		524	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		525
		526	When C<$coderef> is specified, it will be called from C<decode> each
		527	time it decodes a JSON object. The only argument is a reference to the
		528	newly-created hash. If the code references returns a single scalar (which
		529	need not be a reference), this value (i.e. a copy of that scalar to avoid
		530	aliasing) is inserted into the deserialised data structure. If it returns
		531	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		532	original deserialised hash will be inserted. This setting can slow down
		533	decoding considerably.
		534
		535	When C<$coderef> is omitted or undefined, any existing callback will
		536	be removed and C<decode> will not change the deserialised hash in any
		537	way.
		538
		539	Example, convert all JSON objects into the integer 5:
		540
		541	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		542	# returns [5]
		543	$js->decode ('[{}]')
		544	# throw an exception because allow_nonref is not enabled
		545	# so a lone 5 is not allowed.
		546	$js->decode ('{"a":1, "b":2}');
		547
		548	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		549
		550	Works remotely similar to C<filter_json_object>, but is only called for
		551	JSON objects having a single key named C<$key>.
		552
		553	This C<$coderef> is called before the one specified via
		554	C<filter_json_object>, if any. It gets passed the single value in the JSON
		555	object. If it returns a single value, it will be inserted into the data
		556	structure. If it returns nothing (not even C<undef> but the empty list),
		557	the callback from C<filter_json_object> will be called next, as if no
		558	single-key callback were specified.
		559
		560	If C<$coderef> is omitted or undefined, the corresponding callback will be
		561	disabled. There can only ever be one callback for a given key.
		562
		563	As this callback gets called less often then the C<filter_json_object>
		564	one, decoding speed will not usually suffer as much. Therefore, single-key
		565	objects make excellent targets to serialise Perl objects into, especially
		566	as single-key JSON objects are as close to the type-tagged value concept
		567	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		568	support this in any way, so you need to make sure your data never looks
		569	like a serialised Perl hash.
		570
		571	Typical names for the single object key are C<__class_whatever__>, or
		572	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		573	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		574	with real hashes.
		575
		576	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		577	into the corresponding C<< $WIDGET{<id>} >> object:
		578
		579	# return whatever is in $WIDGET{5}:
		580	JSON::XS
		581	->new
		582	->filter_json_single_key_object (__widget__ => sub {
		583	$WIDGET{ $_[0] }
		584	})
		585	->decode ('{"__widget__": 5')
		586
		587	# this can be used with a TO_JSON method in some "widget" class
		588	# for serialisation to json:
		589	sub WidgetBase::TO_JSON {
		590	my ($self) = @_;
		591
		592	unless ($self->{id}) {
		593	$self->{id} = ..get..some..id..;
		594	$WIDGET{$self->{id}} = $self;
		595	}
		596
		597	{ __widget__ => $self->{id} }
		598	}
		599
		600	=item $json = $json->shrink ([$enable])
		601
		602	=item $enabled = $json->get_shrink
		603
		604	Perl usually over-allocates memory a bit when allocating space for
		605	strings. This flag optionally resizes strings generated by either
		606	C<encode> or C<decode> to their minimum size possible. This can save
		607	memory when your JSON texts are either very very long or you have many
		608	short strings. It will also try to downgrade any strings to octet-form
		609	if possible: perl stores strings internally either in an encoding called
		610	UTF-X or in octet-form. The latter cannot store everything but uses less
		611	space in general (and some buggy Perl or C code might even rely on that
		612	internal representation being used).
		613
		614	The actual definition of what shrink does might change in future versions,
		615	but it will always try to save space at the expense of time.
		616
		617	If C<$enable> is true (or missing), the string returned by C<encode> will
		618	be shrunk-to-fit, while all strings generated by C<decode> will also be
		619	shrunk-to-fit.
		620
		621	If C<$enable> is false, then the normal perl allocation algorithms are used.
		622	If you work with your data, then this is likely to be faster.
		623
		624	In the future, this setting might control other things, such as converting
		625	strings that look like integers or floats into integers or floats
		626	internally (there is no difference on the Perl level), saving space.
		627
		628	=item $json = $json->max_depth ([$maximum_nesting_depth])
		629
		630	=item $max_depth = $json->get_max_depth
		631
		632	Sets the maximum nesting level (default C<512>) accepted while encoding
		633	or decoding. If a higher nesting level is detected in JSON text or a Perl
		634	data structure, then the encoder and decoder will stop and croak at that
		635	point.
		636
		637	Nesting level is defined by number of hash- or arrayrefs that the encoder
		638	needs to traverse to reach a given point or the number of C<{> or C<[>
		639	characters without their matching closing parenthesis crossed to reach a
		640	given character in a string.
		641
		642	Setting the maximum depth to one disallows any nesting, so that ensures
		643	that the object is only a single hash/object or array.
		644
		645	If no argument is given, the highest possible setting will be used, which
		646	is rarely useful.
		647
		648	Note that nesting is implemented by recursion in C. The default value has
		649	been chosen to be as large as typical operating systems allow without
		650	crashing.
		651
		652	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		653
		654	=item $json = $json->max_size ([$maximum_string_size])
		655
		656	=item $max_size = $json->get_max_size
		657
		658	Set the maximum length a JSON text may have (in bytes) where decoding is
		659	being attempted. The default is C<0>, meaning no limit. When C<decode>
		660	is called on a string that is longer then this many bytes, it will not
		661	attempt to decode the string but throw an exception. This setting has no
		662	effect on C<encode> (yet).
		663
		664	If no argument is given, the limit check will be deactivated (same as when
		665	C<0> is specified).
		666
		667	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		668
222	=item $json_string = $json->encode ($perl_scalar)	669	=item $json_text = $json->encode ($perl_scalar)
223		670
224	Converts the given Perl data structure (a simple scalar or a reference	671	Converts the given Perl data structure (a simple scalar or a reference
225	to a hash or array) to its JSON representation. Simple scalars will be	672	to a hash or array) to its JSON representation. Simple scalars will be
226	converted into JSON string or number sequences, while references to arrays	673	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined	674	become JSON arrays and references to hashes become JSON objects. Undefined
228	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	675	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.	676	nor C<false> values will be generated.
230		677
231	=item $perl_scalar = $json->decode ($json_string)	678	=item $perl_scalar = $json->decode ($json_text)
232		679
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	680	The opposite of C<encode>: expects a JSON text and tries to parse it,
234	returning the resulting simple scalar or reference. Croaks on error.	681	returning the resulting simple scalar or reference. Croaks on error.
235		682
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	683	JSON numbers and strings become simple Perl scalars. JSON arrays become
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	684	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
238	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	685	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
239		686
		687	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		688
		689	This works like the C<decode> method, but instead of raising an exception
		690	when there is trailing garbage after the first JSON object, it will
		691	silently stop parsing there and return the number of characters consumed
		692	so far.
		693
		694	This is useful if your JSON texts are not delimited by an outer protocol
		695	(which is not the brightest thing to do in the first place) and you need
		696	to know where the JSON text ends.
		697
		698	JSON::XS->new->decode_prefix ("[1] the tail")
		699	=> ([], 3)
		700
240	=back	701	=back
241		702
242	=head1 COMPARISON
243		703
244	As already mentioned, this module was created because none of the existing	704	=head1 INCREMENTAL PARSING
245	JSON modules could be made to work correctly. First I will describe the	705
246	problems (or pleasures) I encountered with various existing JSON modules,	706	In some cases, there is the need for incremental parsing of JSON
247	followed by some benchmark values. JSON::XS was designed not to suffer	707	texts. While this module always has to keep both JSON text and resulting
248	from any of these problems or limitations.	708	Perl data structure in memory at one time, it does allow you to parse a
		709	JSON stream incrementally. It does so by accumulating text until it has
		710	a full JSON object, which it then can decode. This process is similar to
		711	using C<decode_prefix> to see if a full JSON object is available, but
		712	is much more efficient (and can be implemented with a minimum of method
		713	calls).
		714
		715	JSON::XS will only attempt to parse the JSON text once it is sure it
		716	has enough text to get a decisive result, using a very simple but
		717	truly incremental parser. This means that it sometimes won't stop as
		718	early as the full parser, for example, it doesn't detect parenthese
		719	mismatches. The only thing it guarantees is that it starts decoding as
		720	soon as a syntactically valid JSON text has been seen. This means you need
		721	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		722	parsing in the presence if syntax errors.
		723
		724	The following methods implement this incremental parser.
249		725
250	=over 4	726	=over 4
251		727
252	=item JSON 1.07	728	=item [void, scalar or list context] = $json->incr_parse ([$string])
253		729
254	Slow (but very portable, as it is written in pure Perl).	730	This is the central parsing function. It can both append new text and
		731	extract objects from the stream accumulated so far (both of these
		732	functions are optional).
255		733
256	Undocumented/buggy Unicode handling (how JSON handles unicode values is	734	If C<$string> is given, then this string is appended to the already
257	undocumented. One can get far by feeding it unicode strings and doing	735	existing JSON fragment stored in the C<$json> object.
258	en-/decoding oneself, but unicode escapes are not working properly).
259		736
260	No roundtripping (strings get clobbered if they look like numbers, e.g.	737	After that, if the function is called in void context, it will simply
261	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	738	return without doing anything further. This can be used to add more text
262	decode into the number 2.	739	in as many chunks as you want.
263		740
264	=item JSON::PC 0.01	741	If the method is called in scalar context, then it will try to extract
		742	exactly I<one> JSON object. If that is successful, it will return this
		743	object, otherwise it will return C<undef>. If there is a parse error,
		744	this method will croak just as C<decode> would do (one can then use
		745	C<incr_skip> to skip the errornous part). This is the most common way of
		746	using the method.
265		747
266	Very fast.	748	And finally, in list context, it will try to extract as many objects
		749	from the stream as it can find and return them, or the empty list
		750	otherwise. For this to work, there must be no separators between the JSON
		751	objects or arrays, instead they must be concatenated back-to-back. If
		752	an error occurs, an exception will be raised as in the scalar context
		753	case. Note that in this case, any previously-parsed JSON texts will be
		754	lost.
267		755
268	Undocumented/buggy Unicode handling.	756	=item $lvalue_string = $json->incr_text
269		757
270	No roundtripping.	758	This method returns the currently stored JSON fragment as an lvalue, that
		759	is, you can manipulate it. This I<only> works when a preceding call to
		760	C<incr_parse> in I<scalar context> successfully returned an object. Under
		761	all other circumstances you must not call this function (I mean it.
		762	although in simple tests it might actually work, it I<will> fail under
		763	real world conditions). As a special exception, you can also call this
		764	method before having parsed anything.
271		765
272	Has problems handling many Perl values (e.g. regex results and other magic	766	This function is useful in two cases: a) finding the trailing text after a
273	values will make it croak).	767	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		768	(such as commas).
274		769
275	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	770	=item $json->incr_skip
276	which is not a valid JSON string.
277		771
278	Unmaintained (maintainer unresponsive for many months, bugs are not	772	This will reset the state of the incremental parser and will remove the
279	getting fixed).	773	parsed text from the input buffer. This is useful after C<incr_parse>
		774	died, in which case the input buffer and incremental parser state is left
		775	unchanged, to skip the text parsed so far and to reset the parse state.
280		776
281	=item JSON::Syck 0.21	777	=item $json->incr_reset
282		778
283	Very buggy (often crashes).	779	This completely resets the incremental parser, that is, after this call,
		780	it will be as if the parser had never parsed anything.
284		781
285	Very inflexible (no human-readable format supported, format pretty much	782	This is useful if you want ot repeatedly parse JSON objects and want to
286	undocumented. I need at least a format for easy reading by humans and a	783	ignore any trailing data, which means you have to reset the parser after
287	single-line compact format for use in a protocol, and preferably a way to	784	each successful decode.
288	generate ASCII-only JSON strings).
289
290	Completely broken (and confusingly documented) Unicode handling (unicode
291	escapes are not working properly, you need to set ImplicitUnicode to
292	I<different> values on en- and decoding to get symmetric behaviour).
293
294	No roundtripping (simple cases work, but this depends on wether the scalar
295	value was used in a numeric context or not).
296
297	Dumping hashes may skip hash values depending on iterator state.
298
299	Unmaintained (maintainer unresponsive for many months, bugs are not
300	getting fixed).
301
302	Does not check input for validity (i.e. will accept non-JSON input and
303	return "something" instead of raising an exception. This is a security
304	issue: imagine two banks transfering money between each other using
305	JSON. One bank might parse a given non-JSON request and deduct money,
306	while the other might reject the transaction with a syntax error. While a
307	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).
309
310	=item JSON::DWIW 0.04
311
312	Very fast. Very natural. Very nice.
313
314	Undocumented unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).
316
317	Very inflexible.
318
319	No roundtripping.
320
321	Does not generate valid JSON (key strings are often unquoted, empty keys
322	result in nothing being output)
323
324	Does not check input for validity.
325		785
326	=back	786	=back
		787
		788	=head2 LIMITATIONS
		789
		790	All options that affect decoding are supported, except
		791	C<allow_nonref>. The reason for this is that it cannot be made to
		792	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		793	them back to back and still decode them perfectly. This does not hold true
		794	for JSON numbers, however.
		795
		796	For example, is the string C<1> a single JSON number, or is it simply the
		797	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		798	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		799	takes the conservative route and disallows this case.
		800
		801	=head2 EXAMPLES
		802
		803	Some examples will make all this clearer. First, a simple example that
		804	works similarly to C<decode_prefix>: We want to decode the JSON object at
		805	the start of a string and identify the portion after the JSON object:
		806
		807	my $text = "[1,2,3] hello";
		808
		809	my $json = new JSON::XS;
		810
		811	my $obj = $json->incr_parse ($text)
		812	or die "expected JSON object or array at beginning of string";
		813
		814	my $tail = $json->incr_text;
		815	# $tail now contains " hello"
		816
		817	Easy, isn't it?
		818
		819	Now for a more complicated example: Imagine a hypothetical protocol where
		820	you read some requests from a TCP stream, and each request is a JSON
		821	array, without any separation between them (in fact, it is often useful to
		822	use newlines as "separators", as these get interpreted as whitespace at
		823	the start of the JSON text, which makes it possible to test said protocol
		824	with C<telnet>...).
		825
		826	Here is how you'd do it (it is trivial to write this in an event-based
		827	manner):
		828
		829	my $json = new JSON::XS;
		830
		831	# read some data from the socket
		832	while (sysread $socket, my $buf, 4096) {
		833
		834	# split and decode as many requests as possible
		835	for my $request ($json->incr_parse ($buf)) {
		836	# act on the $request
		837	}
		838	}
		839
		840	Another complicated example: Assume you have a string with JSON objects
		841	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		842	[3]>). To parse them, we have to skip the commas between the JSON texts,
		843	and here is where the lvalue-ness of C<incr_text> comes in useful:
		844
		845	my $text = "[1],[2], [3]";
		846	my $json = new JSON::XS;
		847
		848	# void context, so no parsing done
		849	$json->incr_parse ($text);
		850
		851	# now extract as many objects as possible. note the
		852	# use of scalar context so incr_text can be called.
		853	while (my $obj = $json->incr_parse) {
		854	# do something with $obj
		855
		856	# now skip the optional comma
		857	$json->incr_text =~ s/^ \s* , //x;
		858	}
		859
		860	Now lets go for a very complex example: Assume that you have a gigantic
		861	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		862	but you cannot load it into memory fully (this has actually happened in
		863	the real world :).
		864
		865	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		866	can still help you: You implement a (very simple) array parser and let
		867	JSON decode the array elements, which are all full JSON objects on their
		868	own (this wouldn't work if the array elements could be JSON numbers, for
		869	example):
		870
		871	my $json = new JSON::XS;
		872
		873	# open the monster
		874	open my $fh, "<bigfile.json"
		875	or die "bigfile: $!";
		876
		877	# first parse the initial "["
		878	for (;;) {
		879	sysread $fh, my $buf, 65536
		880	or die "read error: $!";
		881	$json->incr_parse ($buf); # void context, so no parsing
		882
		883	# Exit the loop once we found and removed(!) the initial "[".
		884	# In essence, we are (ab-)using the $json object as a simple scalar
		885	# we append data to.
		886	last if $json->incr_text =~ s/^ \s* \[ //x;
		887	}
		888
		889	# now we have the skipped the initial "[", so continue
		890	# parsing all the elements.
		891	for (;;) {
		892	# in this loop we read data until we got a single JSON object
		893	for (;;) {
		894	if (my $obj = $json->incr_parse) {
		895	# do something with $obj
		896	last;
		897	}
		898
		899	# add more data
		900	sysread $fh, my $buf, 65536
		901	or die "read error: $!";
		902	$json->incr_parse ($buf); # void context, so no parsing
		903	}
		904
		905	# in this loop we read data until we either found and parsed the
		906	# separating "," between elements, or the final "]"
		907	for (;;) {
		908	# first skip whitespace
		909	$json->incr_text =~ s/^\s*//;
		910
		911	# if we find "]", we are done
		912	if ($json->incr_text =~ s/^\]//) {
		913	print "finished.\n";
		914	exit;
		915	}
		916
		917	# if we find ",", we can continue with the next element
		918	if ($json->incr_text =~ s/^,//) {
		919	last;
		920	}
		921
		922	# if we find anything else, we have a parse error!
		923	if (length $json->incr_text) {
		924	die "parse error near ", $json->incr_text;
		925	}
		926
		927	# else add more data
		928	sysread $fh, my $buf, 65536
		929	or die "read error: $!";
		930	$json->incr_parse ($buf); # void context, so no parsing
		931	}
		932
		933	This is a complex example, but most of the complexity comes from the fact
		934	that we are trying to be correct (bear with me if I am wrong, I never ran
		935	the above example :).
		936
		937
		938
		939	=head1 MAPPING
		940
		941	This section describes how JSON::XS maps Perl values to JSON values and
		942	vice versa. These mappings are designed to "do the right thing" in most
		943	circumstances automatically, preserving round-tripping characteristics
		944	(what you put in comes out as something equivalent).
		945
		946	For the more enlightened: note that in the following descriptions,
		947	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		948	refers to the abstract Perl language itself.
		949
		950
		951	=head2 JSON -> PERL
		952
		953	=over 4
		954
		955	=item object
		956
		957	A JSON object becomes a reference to a hash in Perl. No ordering of object
		958	keys is preserved (JSON does not preserve object key ordering itself).
		959
		960	=item array
		961
		962	A JSON array becomes a reference to an array in Perl.
		963
		964	=item string
		965
		966	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		967	are represented by the same codepoints in the Perl string, so no manual
		968	decoding is necessary.
		969
		970	=item number
		971
		972	A JSON number becomes either an integer, numeric (floating point) or
		973	string scalar in perl, depending on its range and any fractional parts. On
		974	the Perl level, there is no difference between those as Perl handles all
		975	the conversion details, but an integer may take slightly less memory and
		976	might represent more values exactly than floating point numbers.
		977
		978	If the number consists of digits only, JSON::XS will try to represent
		979	it as an integer value. If that fails, it will try to represent it as
		980	a numeric (floating point) value if that is possible without loss of
		981	precision. Otherwise it will preserve the number as a string value (in
		982	which case you lose roundtripping ability, as the JSON number will be
		983	re-encoded toa JSON string).
		984
		985	Numbers containing a fractional or exponential part will always be
		986	represented as numeric (floating point) values, possibly at a loss of
		987	precision (in which case you might lose perfect roundtripping ability, but
		988	the JSON number will still be re-encoded as a JSON number).
		989
		990	=item true, false
		991
		992	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		993	respectively. They are overloaded to act almost exactly like the numbers
		994	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		995	the C<JSON::XS::is_bool> function.
		996
		997	=item null
		998
		999	A JSON null atom becomes C<undef> in Perl.
		1000
		1001	=back
		1002
		1003
		1004	=head2 PERL -> JSON
		1005
		1006	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1007	truly typeless language, so we can only guess which JSON type is meant by
		1008	a Perl value.
		1009
		1010	=over 4
		1011
		1012	=item hash references
		1013
		1014	Perl hash references become JSON objects. As there is no inherent ordering
		1015	in hash keys (or JSON objects), they will usually be encoded in a
		1016	pseudo-random order that can change between runs of the same program but
		1017	stays generally the same within a single run of a program. JSON::XS can
		1018	optionally sort the hash keys (determined by the I<canonical> flag), so
		1019	the same datastructure will serialise to the same JSON text (given same
		1020	settings and version of JSON::XS), but this incurs a runtime overhead
		1021	and is only rarely useful, e.g. when you want to compare some JSON text
		1022	against another for equality.
		1023
		1024	=item array references
		1025
		1026	Perl array references become JSON arrays.
		1027
		1028	=item other references
		1029
		1030	Other unblessed references are generally not allowed and will cause an
		1031	exception to be thrown, except for references to the integers C<0> and
		1032	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1033	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1034
		1035	encode_json [\0, JSON::XS::true] # yields [false,true]
		1036
		1037	=item JSON::XS::true, JSON::XS::false
		1038
		1039	These special values become JSON true and JSON false values,
		1040	respectively. You can also use C<\1> and C<\0> directly if you want.
		1041
		1042	=item blessed objects
		1043
		1044	Blessed objects are not directly representable in JSON. See the
		1045	C<allow_blessed> and C<convert_blessed> methods on various options on
		1046	how to deal with this: basically, you can choose between throwing an
		1047	exception, encoding the reference as if it weren't blessed, or provide
		1048	your own serialiser method.
		1049
		1050	=item simple scalars
		1051
		1052	Simple Perl scalars (any scalar that is not a reference) are the most
		1053	difficult objects to encode: JSON::XS will encode undefined scalars as
		1054	JSON C<null> values, scalars that have last been used in a string context
		1055	before encoding as JSON strings, and anything else as number value:
		1056
		1057	# dump as number
		1058	encode_json [2] # yields [2]
		1059	encode_json [-3.0e17] # yields [-3e+17]
		1060	my $value = 5; encode_json [$value] # yields [5]
		1061
		1062	# used as string, so dump as string
		1063	print $value;
		1064	encode_json [$value] # yields ["5"]
		1065
		1066	# undef becomes null
		1067	encode_json [undef] # yields [null]
		1068
		1069	You can force the type to be a JSON string by stringifying it:
		1070
		1071	my $x = 3.1; # some variable containing a number
		1072	"$x"; # stringified
		1073	$x .= ""; # another, more awkward way to stringify
		1074	print $x; # perl does it for you, too, quite often
		1075
		1076	You can force the type to be a JSON number by numifying it:
		1077
		1078	my $x = "3"; # some variable containing a string
		1079	$x += 0; # numify it, ensuring it will be dumped as a number
		1080	$x *= 1; # same thing, the choice is yours.
		1081
		1082	You can not currently force the type in other, less obscure, ways. Tell me
		1083	if you need this capability (but don't forget to explain why it's needed
		1084	:).
		1085
		1086	=back
		1087
		1088
		1089	=head1 ENCODING/CODESET FLAG NOTES
		1090
		1091	The interested reader might have seen a number of flags that signify
		1092	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1093	some confusion on what these do, so here is a short comparison:
		1094
		1095	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1096	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1097	control whether C<encode> escapes character values outside their respective
		1098	codeset range. Neither of these flags conflict with each other, although
		1099	some combinations make less sense than others.
		1100
		1101	Care has been taken to make all flags symmetrical with respect to
		1102	C<encode> and C<decode>, that is, texts encoded with any combination of
		1103	these flag values will be correctly decoded when the same flags are used
		1104	- in general, if you use different flag settings while encoding vs. when
		1105	decoding you likely have a bug somewhere.
		1106
		1107	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1108	simply an abstract set of character-codepoint pairs, while an encoding
		1109	takes those codepoint numbers and I<encodes> them, in our case into
		1110	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1111	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1112	the same time, which can be confusing.
		1113
		1114	=over 4
		1115
		1116	=item C<utf8> flag disabled
		1117
		1118	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1119	and expect Unicode strings, that is, characters with high ordinal Unicode
		1120	values (> 255) will be encoded as such characters, and likewise such
		1121	characters are decoded as-is, no canges to them will be done, except
		1122	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1123	respectively (to Perl, these are the same thing in strings unless you do
		1124	funny/weird/dumb stuff).
		1125
		1126	This is useful when you want to do the encoding yourself (e.g. when you
		1127	want to have UTF-16 encoded JSON texts) or when some other layer does
		1128	the encoding for you (for example, when printing to a terminal using a
		1129	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1130	to UTF-8 encode your data first and have Perl encode it another time).
		1131
		1132	=item C<utf8> flag enabled
		1133
		1134	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1135	characters using the corresponding UTF-8 multi-byte sequence, and will
		1136	expect your input strings to be encoded as UTF-8, that is, no "character"
		1137	of the input string must have any value > 255, as UTF-8 does not allow
		1138	that.
		1139
		1140	The C<utf8> flag therefore switches between two modes: disabled means you
		1141	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1142	octet/binary string in Perl.
		1143
		1144	=item C<latin1> or C<ascii> flags enabled
		1145
		1146	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1147	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1148	characters as specified by the C<utf8> flag.
		1149
		1150	If C<utf8> is disabled, then the result is also correctly encoded in those
		1151	character sets (as both are proper subsets of Unicode, meaning that a
		1152	Unicode string with all character values < 256 is the same thing as a
		1153	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1154	the same thing as an ASCII string in Perl).
		1155
		1156	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1157	regardless of these flags, just some more characters will be escaped using
		1158	C<\uXXXX> then before.
		1159
		1160	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1161	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1162	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1163	a subset of Unicode), while ASCII is.
		1164
		1165	Surprisingly, C<decode> will ignore these flags and so treat all input
		1166	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1167	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1168	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1169
		1170	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1171	they only govern when the JSON output engine escapes a character or not.
		1172
		1173	The main use for C<latin1> is to relatively efficiently store binary data
		1174	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1175
		1176	The main use for C<ascii> is to force the output to not contain characters
		1177	with values > 127, which means you can interpret the resulting string
		1178	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1179	8-bit-encoding, and still get the same data structure back. This is useful
		1180	when your channel for JSON transfer is not 8-bit clean or the encoding
		1181	might be mangled in between (e.g. in mail), and works because ASCII is a
		1182	proper subset of most 8-bit and multibyte encodings in use in the world.
		1183
		1184	=back
		1185
		1186
		1187	=head2 JSON and YAML
		1188
		1189	You often hear that JSON is a subset of YAML. This is, however, a mass
		1190	hysteria(*) and very far from the truth (as of the time of this writing),
		1191	so let me state it clearly: I<in general, there is no way to configure
		1192	JSON::XS to output a data structure as valid YAML> that works in all
		1193	cases.
		1194
		1195	If you really must use JSON::XS to generate YAML, you should use this
		1196	algorithm (subject to change in future versions):
		1197
		1198	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1199	my $yaml = $to_yaml->encode ($ref) . "\n";
		1200
		1201	This will I<usually> generate JSON texts that also parse as valid
		1202	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1203	lengths that JSON doesn't have and also has different and incompatible
		1204	unicode handling, so you should make sure that your hash keys are
		1205	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1206	you do not have characters with codepoint values outside the Unicode BMP
		1207	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1208	strings (which JSON::XS does not I<currently> generate, but other JSON
		1209	generators might).
		1210
		1211	There might be other incompatibilities that I am not aware of (or the YAML
		1212	specification has been changed yet again - it does so quite often). In
		1213	general you should not try to generate YAML with a JSON generator or vice
		1214	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1215	high that you will run into severe interoperability problems when you
		1216	least expect it.
		1217
		1218	=over 4
		1219
		1220	=item (*)
		1221
		1222	I have been pressured multiple times by Brian Ingerson (one of the
		1223	authors of the YAML specification) to remove this paragraph, despite him
		1224	acknowledging that the actual incompatibilities exist. As I was personally
		1225	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1226	educate people about these issues, so others do not run into the same
		1227	problem again and again. After this, Brian called me a (quote)I<complete
		1228	and worthless idiot>(unquote).
		1229
		1230	In my opinion, instead of pressuring and insulting people who actually
		1231	clarify issues with YAML and the wrong statements of some of its
		1232	proponents, I would kindly suggest reading the JSON spec (which is not
		1233	that difficult or long) and finally make YAML compatible to it, and
		1234	educating users about the changes, instead of spreading lies about the
		1235	real compatibility for many I<years> and trying to silence people who
		1236	point out that it isn't true.
		1237
		1238	=back
		1239
327		1240
328	=head2 SPEED	1241	=head2 SPEED
329		1242
330	It seems that JSON::XS is surprisingly fast, as shown in the following	1243	It seems that JSON::XS is surprisingly fast, as shown in the following
331	tables. They have been generated with the help of the C<eg/bench> program	1244	tables. They have been generated with the help of the C<eg/bench> program
332	in the JSON::XS distribution, to make it easy to compare on your own	1245	in the JSON::XS distribution, to make it easy to compare on your own
333	system.	1246	system.
334		1247
335	First is a comparison between various modules using a very simple JSON	1248	First comes a comparison between various modules using
		1249	a very short single-line JSON string (also available at
		1250	L<http://dist.schmorp.de/misc/json/short.json>).
		1251
		1252	{"method": "handleMessage", "params": ["user1",
		1253	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1254	true, false]}
		1255
336	string, showing the number of encodes/decodes per second (JSON::XS is	1256	It shows the number of encodes/decodes per second (JSON::XS uses
337	the functional interface, while JSON::XS/2 is the OO interface with	1257	the functional interface, while JSON::XS/2 uses the OO interface
338	pretty-printing and hashkey sorting enabled).	1258	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1259	shrink). Higher is better:
339		1260
340	module | encode | decode |	1261	module | encode | decode |
341	-----------|------------|------------|	1262	-----------|------------|------------|
342	JSON | 14006 | 6820 |	1263	JSON 1.x | 4990.842 | 4088.813 |
343	JSON::DWIW | 200937 | 120386 |	1264	JSON::DWIW | 51653.990 | 71575.154 |
344	JSON::PC | 85065 | 129366 |	1265	JSON::PC | 65948.176 | 74631.744 |
345	JSON::Syck | 59898 | 44232 |	1266	JSON::PP | 8931.652 | 3817.168 |
346	JSON::XS | 1171478 | 342435 |	1267	JSON::Syck | 24877.248 | 27776.848 |
347	JSON::XS/2 | 730760 | 328714 |	1268	JSON::XS | 388361.481 | 227951.304 |
		1269	JSON::XS/2 | 227951.304 | 218453.333 |
		1270	JSON::XS/3 | 338250.323 | 218453.333 |
		1271	Storable | 16500.016 | 135300.129 |
348	-----------+------------+------------+	1272	-----------+------------+------------+
349		1273
350	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1274	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1275	about three times faster on decoding, and over forty times faster
351	times faster than JSON, even with pretty-printing and key sorting.	1276	than JSON, even with pretty-printing and key sorting. It also compares
		1277	favourably to Storable for small amounts of data.
352		1278
353	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1279	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
354	search API (http://nanoref.com/yahooapis/mgPdGg):	1280	search API (L<http://dist.schmorp.de/misc/json/long.json>).
355		1281
356	module | encode | decode |	1282	module | encode | decode |
357	-----------|------------|------------|	1283	-----------|------------|------------|
358	JSON | 673 | 38 |	1284	JSON 1.x | 55.260 | 34.971 |
359	JSON::DWIW | 5271 | 770 |	1285	JSON::DWIW | 825.228 | 1082.513 |
360	JSON::PC | 9901 | 2491 |	1286	JSON::PC | 3571.444 | 2394.829 |
361	JSON::Syck | 2360 | 786 |	1287	JSON::PP | 210.987 | 32.574 |
362	JSON::XS | 37398 | 3202 |	1288	JSON::Syck | 552.551 | 787.544 |
363	JSON::XS/2 | 13765 | 3153 |	1289	JSON::XS | 5780.463 | 4854.519 |
		1290	JSON::XS/2 | 3869.998 | 4798.975 |
		1291	JSON::XS/3 | 5862.880 | 4798.975 |
		1292	Storable | 4445.002 | 5235.027 |
364	-----------+------------+------------+	1293	-----------+------------+------------+
365		1294
366	Again, JSON::XS leads by far in the encoding case, while still beating	1295	Again, JSON::XS leads by far (except for Storable which non-surprisingly
367	every other module in the decoding case.	1296	decodes faster).
368		1297
369	Last example is an almost 8MB large hash with many large binary values	1298	On large strings containing lots of high Unicode characters, some modules
370	(PNG files), resulting in a lot of escaping:	1299	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1300	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1301	to decode or encode properly, so it was impossible to prepare a fair
		1302	comparison table for that case.
		1303
		1304
		1305	=head1 SECURITY CONSIDERATIONS
		1306
		1307	When you are using JSON in a protocol, talking to untrusted potentially
		1308	hostile creatures requires relatively few measures.
		1309
		1310	First of all, your JSON decoder should be secure, that is, should not have
		1311	any buffer overflows. Obviously, this module should ensure that and I am
		1312	trying hard on making that true, but you never know.
		1313
		1314	Second, you need to avoid resource-starving attacks. That means you should
		1315	limit the size of JSON texts you accept, or make sure then when your
		1316	resources run out, that's just fine (e.g. by using a separate process that
		1317	can crash safely). The size of a JSON text in octets or characters is
		1318	usually a good indication of the size of the resources required to decode
		1319	it into a Perl structure. While JSON::XS can check the size of the JSON
		1320	text, it might be too late when you already have it in memory, so you
		1321	might want to check the size before you accept the string.
		1322
		1323	Third, JSON::XS recurses using the C stack when decoding objects and
		1324	arrays. The C stack is a limited resource: for instance, on my amd64
		1325	machine with 8MB of stack size I can decode around 180k nested arrays but
		1326	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1327	to free the temporary). If that is exceeded, the program crashes. To be
		1328	conservative, the default nesting limit is set to 512. If your process
		1329	has a smaller stack, you should adjust this setting accordingly with the
		1330	C<max_depth> method.
		1331
		1332	Something else could bomb you, too, that I forgot to think of. In that
		1333	case, you get to keep the pieces. I am always open for hints, though...
		1334
		1335	Also keep in mind that JSON::XS might leak contents of your Perl data
		1336	structures in its error messages, so when you serialise sensitive
		1337	information you might want to make sure that exceptions thrown by JSON::XS
		1338	will not end up in front of untrusted eyes.
		1339
		1340	If you are using JSON::XS to return packets to consumption
		1341	by JavaScript scripts in a browser you should have a look at
		1342	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1343	you are vulnerable to some common attack vectors (which really are browser
		1344	design bugs, but it is still you who will have to deal with it, as major
		1345	browser developers care only for features, not about getting security
		1346	right).
		1347
		1348
		1349	=head1 THREADS
		1350
		1351	This module is I<not> guaranteed to be thread safe and there are no
		1352	plans to change this until Perl gets thread support (as opposed to the
		1353	horribly slow so-called "threads" which are simply slow and bloated
		1354	process simulations - use fork, it's I<much> faster, cheaper, better).
		1355
		1356	(It might actually work, but you have been warned).
		1357
371		1358
372	=head1 BUGS	1359	=head1 BUGS
373		1360
374	While the goal of this module is to be correct, that unfortunately does	1361	While the goal of this module is to be correct, that unfortunately does
375	not mean its bug-free, only that I think its design is bug-free. It is	1362	not mean it's bug-free, only that I think its design is bug-free. If you
376	still very young and not well-tested. If you keep reporting bugs they will	1363	keep reporting bugs they will be fixed swiftly, though.
377	be fixed swiftly, though.	1364
		1365	Please refrain from using rt.cpan.org or any other bug reporting
		1366	service. I put the contact address into my modules for a reason.
378		1367
379	=cut	1368	=cut
380		1369
		1370	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1371	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1372
		1373	sub true() { $true }
		1374	sub false() { $false }
		1375
		1376	sub is_bool($) {
		1377	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1378	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1379	}
		1380
		1381	XSLoader::load "JSON::XS", $VERSION;
		1382
		1383	package JSON::XS::Boolean;
		1384
		1385	use overload
		1386	"0+" => sub { ${$_[0]} },
		1387	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1388	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1389	fallback => 1;
		1390
381	1;	1391	1;
		1392
		1393	=head1 SEE ALSO
		1394
		1395	The F<json_xs> command line utility for quick experiments.
382		1396
383	=head1 AUTHOR	1397	=head1 AUTHOR
384		1398
385	Marc Lehmann <schmorp@schmorp.de>	1399	Marc Lehmann <schmorp@schmorp.de>
386	http://home.schmorp.de/	1400	http://home.schmorp.de/

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